1. Field of the Invention
The invention relates to a vehicle in which engine starting control is performed when an engine is started while the vehicle is running with power of a motor, and also relates to a control method for the vehicle.
2. Description of Related Art
A vehicle including an engine, a motor, and an engine clutch that selectively couples the engine to a power transmission path from the motor to driving wheels is known. A control system for this type of vehicle is disclosed in, for example, Japanese Patent Application Publication No. 2011-016390 (JP 2011-016390 A). The control system for the vehicle disclosed in JP 2011-016390 A performs engine starting control for temporarily releasing the engine clutch during a period from the beginning of engagement of the engine clutch to full engagement thereof, when the engine is started while the vehicle is running only with power of the motor. More specifically, under the engine starting control, the control system initially increases the engine speed by partially engaging the engine clutch while allowing the clutch to slip, and releases the engine clutch when the engine speed reaches a predetermined rotational speed at which it is determined that the engine is able to rotate by itself. Then, the control system for the vehicle further increases the engine speed in a condition where the engine clutch is released. The control system starts an operation to engage the engine clutch after the engine speed becomes higher than the motor speed, and fully engages the engine clutch when the engine speed becomes equal to the motor speed.
The engine starting control performed when the engine is started while the vehicle is running with power of the motor is considerably effective in reducing shocks when the engine is started. In starting the engine under the engine starting control, the engine speed needs to be increased from an engine stop condition until it becomes equal to the motor speed. The increase of the engine speed is assisted by torque of the motor while the engine clutch is partially engaged while slipping. However, the engine speed is basically increased by engine torque. It follows that, when the motor speed is high, such as when the vehicle is running with power of the motor at a high vehicle speed, the engine speed needs to be increased by a large amount to the motor speed, from the engine stop condition, when the engine is started. Namely, a period of time it takes from the time when engine starting is initiated to the time when the engine speed becomes equal to the motor speed, namely, a period of time it takes from the time when engine starting is initiated to the time when the engine clutch is fully engaged, is prolonged. As a result, the driveability may deteriorate; more specifically, the driver may feel uncomfortable, or the response of the driving force may be reduced. This problem has not been publicly known.